Cie igcse physics forces hookes law
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CIE IGCSE PHYSICS Forces – Hookes Law. 23 rd November 2011. Physics for IGCSE Physics pages 60-61. 1.5 Effects of Forces Core • State that a force may produce a change in size and shape of a body • Plot extension/load graphs and describe the associated experimental procedure Supplement

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CIE IGCSE PHYSICS Forces – Hookes Law

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Cie igcse physics forces hookes law

CIE IGCSE PHYSICSForces – Hookes Law

23rd November 2011

Physics for IGCSE Physics pages 60-61


Cie igcse specification

1.5 Effects of Forces

Core

• State that a force may produce a change in size and shape of a body

• Plot extension/load graphs and describe the associated experimental procedure

Supplement

• Interpret extension/load graphs

• State Hooke’s Law and recall and use the expression F = k x

F= Force k = spring constant x= extension length

• Recognise the significance of the term ‘limit of proportionality’ for an extension/load graph

CIE IGCSE Specification


Changing shape

Changing shape

Force can also change the shape of an object.

A stretching force puts an object such as a wire or spring under tension.

A squashing force puts an object under compression.


Hooke s law glossary

Hooke’s Law Glossary

  • Elastic materials return to their original shape when the forces on them are removed.

  • Plastic materials retain their new shape, when forces are removed

  • Hooke’s Law - The extension of a spring or wire is directly proportional to the force applied provided the limit of proportionality is not exceeded.

  • Spring constant is the gradient of the force (x- axis) against extension (y-axis) the gradient is the spring constant Units N/m

  • A stretching force puts an object such as a wire or spring under tension

  • The limit of proportionality is the is the point  beyond which Hooke’s law is no longer true when stretching a material.

  • The elastic limit is the point beyond which the material you are stretching becomes permanently stretched so that the material does not return to its original length when the force is removed.

  • A squashing force puts an object under compression.


Cie igcse physics forces hookes law

Brittle materials such as glass do not change shape easily and break before noticeably stretching.

Resilient materials do not break easily.


Cie igcse physics forces hookes law

Elastic materials return to their original shape when the forces on them are removed.

Plastic materials retain their new shape.


Stretching springs

Stretching Springs

Experimental procedure:

1. Place the weight holder only on the spring and note the position of the pin against the metre rule.

2. Add 1N (100g) to the holder and note the new position of the pin.

3. Calculate the extension of the spring.

4. Repeat stages 1 to 3 for 2N, 3N, 4N, 5N and 6N. DO NOT EXCEED 6N.

spring

weights

pin

metre rule


Typical results

Typical results


Force against extension graph

Force against extension graph

Force (N)

0

Extension (mm)

0


Hooke s law

Hooke’s law

Hooke’s law states that the extension of a spring force is proportional to the force used to stretch the spring.

‘Proportional’ means that if the force is doubled then the extension also doubles.

The line on a graph of force against extension will be a straight AND go through the origin.


Cie igcse physics forces hookes law

Hooke’s Law

  • When a material obeys Hooke’s Law, the force is proportional to the extension of the material.

  • Force  Extension

  • F  x

  • This leads to the equation:

  • F = kx

  • Where k is a measure of the stiffness of the sample – the gradient of a force – extension graph.


Cie igcse physics forces hookes law

Force-Extension Graphs

x

10

x

x

x

x

x

Force (N)

5

x

x

x

x

x

0

0

0.25

0.5

Extension (m)


Cie igcse physics forces hookes law

Extension Work

  • Sketch a force-extension graph (the line should be roughly halfway between your axes).

  • Sketch a second line for a stiffer spring (harder to stretch).

  • Sketch a third line for a less stiff spring (easier to stretch).

  • Explain each line, relating the force to the extension.


Cie igcse physics forces hookes law

Force-Extension Graphs


Cie igcse physics forces hookes law

Force-Extension Graphs


Cie igcse physics forces hookes law

Force-Extension Graphs


Question

Question

A spring of original length 150mm is extended by 30mm by a force of 4N. Calculate the length of the spring if a force of 12N is applied.

12N is three times 4N

Therefore the new extension should be 3 x 30mm

= 90mm

New spring length = 150mm + 90mm

= 240mm


Elastic limit

The right hand spring has been stretched beyond its elastic limit

Elastic limit

Up to a certain extension if the force is removed the spring will return to its original length. The spring is behaving elastically.

If this critical extension is exceeded, known as the elastic limit, the spring will be permanently stretched.

Hooke’s law is no longer obeyed by the spring if its elastic limit is exceeded.


Force against extension graph if the elastic limit is exceeded

Force against extension graph if the elastic limit is exceeded

Force (N)

elastic limit

0

Extension (mm)

0


Stretching an elastic band

Stretching an elastic band

Force

0

Extension

0

An elastic band does not obey Hooke’s law.


Cie igcse physics forces hookes law

Choose appropriate words to fill in the gaps below:

Hooke’s law states that when a wire or spring is _________ the increase in length or _________ is proportional to the load ______ applied.

This law is not obeyed if the spring is taken beyond its ______ limit after which it will become _____________ stretched.

A ________ band does not obey Hooke’s law.

A graph illustrating Hooke’s law will have a line that is ___________ and passes through the _______.

stretched

extension

force

elastic

permanently

rubber

straight

origin

WORD SELECTION:

stretched

elastic

permanently

extension

origin

force

rubber

straight


Online simulations

Effect of forces on motion using a space module - Freezeray.com

Force combination balloon game - eChalk

Electric & Magnetic Forces - 'Whys Guy' Video Clip (3:30mins) - Shows Charged Balloon & Effect of a magnet on a TV screen.

Resultant of two forces - Fendt

Forces on objects immersed in liquids - NTNU

BBC KS3 Bitesize Revision:

What is a force

Balanced forces

Unbalanced forces

BBC AQA GCSE Bitesize Revision:

Resultant force

Types of forces

Online Simulations

Vector Addition - PhET - Learn how to add vectors. Drag vectors onto a graph, change their length and angle, and sum them together. The magnitude, angle, and components of each vector can be displayed in several formats.

Representing vectors - eChalk

Vectors & Scalars - eChalk

Vector addition - eChalk

Vector Chains - eChalk

Fifty-Fifty Game on Vectors & Scalars - by KT - Microsoft WORD

Vector addition - Explore Science

Stretching Springs - PhET - A realistic mass and spring laboratory. Hang masses from springs and adjust the spring stiffness and damping. You can even slow time. Transport the lab to different planets. A chart shows the kinetic, potential, and thermal energy for each spring.


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